Paper-making machines are designed to produce paper at high production rates, and therefore are equipped with rapidly moving forming wires. Vertical paper making machines such as the Bel Baie type vertical formers manufactured by the Beloit Corporation utilize two opposed forming wires between which the forming sheet of paper is sandwiched.
In some cases, the turn shoe assemblies on the wet end sections of vertical formers rely on stationary convex ceramic turning shoes to guide and turn the forming wire as it rotates or travels around the machine. Such ceramic turning shoes are advantageous for various reasons, including quality enhancement to the paper, ease of maintenance due to fewer moving parts than traditional drum turning assemblies, and the increased durability of the ceramic material.
The forming wire in a vertical former travels around the stationary turn shoes under tension so that the inner surface of the wire moves over the smooth convex surface of the turn shoe as the forming wire changes direction. This creates a nip at the point where the wire meets each turning shoe. During the paper-making process, debris may fall onto the inner surface of the wire and accumulate thereon. Such debris often includes rust chips that fall onto the wire from other parts of the machine, dried hard stock that falls onto the wire, or accumulations of fiber. This typically occurs during start-up of the machine, but may occur at any time. As the rapidly moving wire moves past the stationary turning shoes, debris that falls onto the wire accumulates and becomes trapped at the nip between the shoes and the wire. This can lead to excessive wear on the wire, which is typically formed of plastics, such as polyester and nylon, shortening the useful life of the wire. In extreme cases, hard pieces of debris caught at the nip between the turning shoe and the wire may be pushed through the taut wire, producing a hole in the wire that reduces the quality of the paper and eventually requires replacement of the wire. Such debris may in some cases also damage the ceramic turning shoes.
Prior attempts at removing debris from the inner surface of the forming wire upstream from the turning shoes have been largely unsuccessful. For example, hosing the inner surface of the wire with water during start-up has been used as a method of removing debris, but is unreliable.
Therefore, there is a need for an improved apparatus and method that reliably removes debris from the inner surface of forming wires used in paper-making machines that have stationary ceramic turn shoes.